The present invention relates to a lithium ion battery, and particularly relates to a thin film solid state lithium ion secondary battery in which all layers that are formed on a substrate and compose the battery are able to be formed by dry process, and a method of manufacturing the same.
A lithium ion secondary battery has a higher energy density and more superior charge and discharge cycle characteristics compared to other secondary batteries, and thus the lithium ion secondary battery is widely used as an electric power source of a mobile electronic device. In the lithium ion secondary battery using an electrolytic solution as an electrolyte, reducing its size and its thickness is limited. Thus, a polymer battery using a gel electrolyte and a thin film solid state battery using a solid electrolyte have been developed.
In the polymer battery using the gel electrolyte, reducing its thickness and its size is more easily enabled than in batteries using an electrolytic solution. However, reducing its thickness and its size is limited in order to securely seal the gel electrolyte. The thin film solid state battery using the solid electrolyte is composed of layers formed on a substrate, that is, is composed of an anode current collector film, an anode active material film, a solid electrolyte film, a cathode active material film, and a cathode current collector film. In the thin film solid state battery using the solid electrolyte, its thickness and its size are able to be more decreased by using a thin substrate or a thin solid electrolyte film as a substrate. Further, in the thin film solid state battery, a solid nonaqueous electrolyte is able to be used as an electrolyte and the all respective layers composing the battery are able to be solid. Thus, there is no possibility that deterioration is caused by leakage, and a member for preventing leakage and corrosion is not necessitated differently from in the polymer battery using the gel electrolyte. Accordingly, in the thin film solid state battery, the manufacturing process is able to be simplified, and safety thereof may be high.
In the case where decreasing its size and its thickness is realized, the thin film solid state battery is able to be built onto an electric circuit board in a manner of on-chip. Further, in the case where a polymer substrate is used as an electric circuit board and the thin film solid state battery is formed thereon, a flexible battery is able to be formed. Such a flexible battery is able to be built in a card electronic money, an RF ID tag and the like.
For the thin film solid state lithium ion secondary battery in which the all layers composing the battery are formed from solid described above, many reports have been made.
First, in the after-mentioned Patent document 1 entitled “SEMICONDUCTOR SUBSTRATE MOUNTED SECONDARY BATTERY,” the following description is given.
In an embodiment of Patent document 1, an insulating film is formed on a silicon substrate, a wiring electrode is formed thereon, and a cathode and an anode are respectively arranged in line on the wiring electrode. That is, the cathode and the anode are not layered. Since such arrangement is adopted, the thickness of the battery itself is able to be more decreased. Further, in the case of this embodiment, the substrate is able to be changed to an insulator.
Further, in the after-mentioned Patent document 2 entitled “THIN FILM SOLID STATE SECONDARY BATTERY AND COMPOUND DEVICE INCLUDING THE SAME,” the following description is given.
A lithium ion thin film solid state secondary battery of Patent document 2 is formed by sequentially layering a current collector layer on a cathode side (cathode current collector layer), a cathode active material layer, a solid electrolyte layer, an anode active material layer, a current collector layer on an anode side (anode current collector layer), and a moisture barrier film on a substrate. It is to be noted that the lamination on the substrate may be made in the order of the current collector layer on the anode side, the anode active material layer, the solid electrolyte layer, the cathode active material layer, the current collector layer on the cathode side, and the moisture barrier film.
As the substrate, glass, semiconductor silicon, ceramic, stainless steel, a resin substrate or the like is able to be used. As the resin substrate, polyimide, PET (polyethylene terephthalate) or the like is able to be used. Further, as long as handling is available without deformation, a flexible thin film is able to be used as the substrate. The foregoing substrates preferably have additional characteristics such as characteristics to improve transparency, characteristics to prevent diffusion of alkali element such as Na, characteristics to improve heat resistance, and gas barrier characteristics. To this end, a substrate in which a thin film such as SiO2 and TiO2 is formed on the surface by sputtering method or the like may be used.
Further, in the after-mentioned Patent document 3 entitled “METHOD OF MANUFACTURING ALL SOLID STATE LITHIUM SECONDARY BATTERY AND ALL SOLID STATE LITHIUM SECONDARY BATTERY,” a description is given of an all solid state lithium secondary battery capable of avoiding short circuit between a cathode film and an anode film in a battery edge section.
Further, in the after-mentioned Non patent document 1, a description is given of fabricating a Li battery composed of a thin film formed by sputtering method.
As an anode of the existing bulk Li batteries, carbon is widely used. Further, though it has been considered to use other material, practical usage may be difficult in terms of durability and the like. For example, in experiments of the lithium ion secondary batteries, a Li metal is often used as a high capacity material for composing the anode, and thereby high electric potential is obtained. The Li metal has not been practically used as a component material of the anode for the following reason. That is, in the case where Li is precipitated on the metal surface on the anode side, Li is grown in the form of needles, activity is lowered, battery characteristics rapidly deteriorate, and there is a problem in durability.
In the after-mentioned Non patent document 2, a description is given of a lithium free thin film battery.